New fossil from China changes much of what we know about early echinoderm evolution

A new stemmed echinoderm from the Furongian of China and the origin of Glyptocystitida (Blastozoa, Echinodermata)
S. Zamora, C.D. Sumrall, X-J. Zhu, and B. Lefebvre
Summarized by Time Scavengers contributor, Sarah Sheffield

What data were used? A single, beautifully preserved echinoderm (relatives of sea stars and sea urchins) fossil from South China, named Sanducystis sinensis. Rhombiferans are extinct types of echinoderms with diamond shaped plates.

Sanducystis sinensis, a new rhombiferan echinoderm fossil from China tells us a lot about the evolution of echinoderms from an important time in Earth’s history, the late Cambrian (~500-480 million years ago).

Methods: The new rhombiferan fossil was examined for all preserved features on its body; these features were ‘coded’ as characters for an evolutionary analysis. An example of a character: Does this have a stem? Yes=0; No=1. These characters were also used to code multiple other species of rhombiferan echinoderms. The reason for this was to figure out to what Sanducystis sinensis was most closely related. Computer programs, like PAUP*, take all of the characters coded and determine evolutionary relationships, based on the shared similarities between the species used in the analysis.

Results: Sanducystis sinensis falls within a large group of rhombiferan echinoderms called “Glyptocystitida” (similar to how humans are a large group of mammals). It’s an important find, as its place within the evolutionary tree of life is representative of a type of transitional fossil between a group of early rhombiferans that lack specialized breathing apparati and a group of more advanced, or derived, rhombiferans.

Why is this study important? This study paints a more complete story of how rhombiferans evolved through the Cambrian. It was not clear how the transition from rhombiferans without specialized breathing apparati gave rise to the more derived forms that we saw after the late Cambrian. This new find, Sanducystis sinensis, helps us to understand how that transition happened.

Big picture: Rocks from the late Cambrian (~500-480 million years ago) are very rare worldwide; this, of course, means that there are also very few fossils from this time as well. The late Cambrian is a very important time in Earth’s history, however, so finding fossils preserved from this time is critical towards understanding the evolution of life. Fossil finds, such as Sanducystis sinensis, have the potential to completely change what we currently know about how and when different groups of organisms on Earth evolved.

Citation: Zamora, S., Sumrall, C.D., Zhu, X-J., Lefebvre, B., 2016, A new stemmed echinoderm from the Furongian of China and the origin of Glyptocystitida (Blastozoa, Echinodermata): Geological Magazine, p. 1-11.

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